1) Field of the Invention
This invention relates to a method and apparatus for processing semiconductor substrates, particularly to a metrology tool for use in processing semiconductor substrates.
2) Discussion of Related Art
Integrated circuits are formed on semiconductor substrates such as wafers. The formation of the integrated circuits may include numerous processing steps such as deposition of various layers, etching some of the layers, and multiple bakes. The integrated circuits are then separated into individual microelectronic dice, which are packaged and attached to circuit boards.
During the various processing steps involved in the creation of the integrated circuits, various layers of different materials, such as conductors, dielectrics, and semiconductor, are formed on the surface of the wafer where the integrated circuits are being formed. The manufacturers of the integrated circuits often test the composition of the various layers to ensure that the proper materials are being deposited on the substrates.
The machines used to test the composition of the layers are often referred to as “metrology tools.” The metrology tools emit electromagnetic radiation, such as x-rays from an x-ray source, which are deflected off a particular region of a substrate that is being tested. The metrology tools make use of analysis protocols, such as X-ray Photoelectron Spectroscopy (XPS), Total Reflection X-ray Fluorescence (TXRF), and ellipsometry, to measure particular characteristics of the substrate. If, for example, XPS is used, photoelectrons, or electrons, are emitted from the substrate and captured by an electron spectrometer or hemispherical analyzer. The analyzer determines the composition of the region of the substrate by analyzing the kinetic energy, or speed, of the photoelectrons.
The metrology tools typically use a robot to remove the substrate from a load-lock chamber and a separate “stage” to position the substrate into an analytical position under the x-ray source.
The need for the separate stage adds to the complexity of the metrology tool and increases the costs of the manufacturing the integrated circuits. Additionally, the stage moves in an unpredictable manner and the substrate is often not perfectly centered on the stage, which adds to the difficulty of locating the exact position of the particular features on the substrate that are to be tested. If the electromagnetic radiation is misdirected, the integrated circuits could be damaged.